The present invention relates generally to spacecraft engineering and design. More particularly, the present invention relates to a spacecraft actuator that can function as a momentum wheel, a reaction wheel or a gimbal. More specifically, the present invention relates to battery storage and fuel storage.
Spacecraft, satellites, or other vehicles in orbit experience a number of factors that can cause unwanted changes in attitude. Control systems, also known as attitude control systems, are utilized to control and adjust the attitude of a spacecraft. These control systems can include various rotating inertia members such as reaction wheels, control momentum gyroscopes and similar actuators. Current spacecraft employ at least three actuator wheels functioning as momentum wheels and/or reaction wheels.
A reaction wheel is a type of attitude control device that can be used in attitude control systems to exchange angular momentum with a spacecraft. They do not move the spacecraft from one place to another. Reaction wheels can only rotate a spacecraft around its center of mass by very small amounts. To this end, a reaction wheel includes a flywheel mounted on a frame or housing of the spacecraft. An electric motor produces a torque along a spin axis of the flywheel so that the flywheel rotates to produce a force that opposes motion in one plane. This is accomplished by equipping the spacecraft with a controller to control the electric motor and resulting rotation of the flywheel. When the flywheel's rotational velocity is changed, the spacecraft counter-rotates proportionately through conservation of angular momentum.
A rotating wheel is sometimes operated as a momentum wheel when it is rotated at a constant (or near-constant) rotational velocity in order to imbue a spacecraft with a large amount of stored angular momentum. As such, the spacecraft's rotational dynamics are altered so that disturbance torques perpendicular to one axis of the spacecraft (the axis parallel to the flywheel's spin axis) do not result directly in spacecraft angular motion about the same axis as the disturbance torque. Instead, they result in angular motion of that spacecraft axis about a perpendicular axis. This stabilizes the spacecraft axis to point in a nearly-fixed direction, allowing for a less-complicated attitude control system.
A control momentum gyroscope is another type of attitude control device. A control momentum gyroscope typically includes a spinning rotor, for example, and a flywheel mounted on one or more motorized gimbals that tilt the rotor's angular momentum. As the rotor tilts, the changing angular momentum causes a gyroscopic torque that rotates the spacecraft. The spin axis of the control momentum gyroscope can be changed by moving the rotor using the gimbal assembly. Control momentum gyroscopes differ from reaction wheels in that reaction wheels apply torque simply by changing rotor spin speed, while control momentum gyroscopes tilt the rotor's spin axis without necessarily changing its spin speed.
Even more recently, spacecraft have been designed by combining homogeneous cells, also referred to herein as satlets. The term “satlet” refers to a cell of a cell-based spacecraft where each satlet possesses the traditional architecture of a spacecraft including structure, power, fuel, attitude control and determination, satellite processing, etc. Thus, preferably each satlet has its own frame that incorporates multiple spacecraft subsystems including solar panels, batteries, one or more actuator wheels (functioning as a momentum wheel and/or reaction wheel), image sensors, thermal control systems, a propulsion system including a fuel tank and thrusters, and electronics for command and data handling, data sharing, attitude control and position control. Preferably, each satlet is substantially identical so as to be manufactured inexpensively and quickly. The satlets are aggregated together to form a single geographically co-located spacecraft which can increase performance with increased numbers to support payload functions such as communications and surveillance.
Unfortunately, reaction wheels, momentum wheels, and gimbals (collectively referred to herein as “actuator wheels”) consume significant space and add substantial weight to a spacecraft and particularly on a satlet. Similarly, batteries and fuel tanks take up significant space and add substantial weight to spacecraft and particularly to a satlet.
Thus, with the smaller satlet design, it would be desirable to provide a spacecraft actuator wheel that can function as a momentum wheel, a reaction wheel or a gimbal which integrates batteries and a fuel tank.